PERC 2009 Abstract Detail Page

Student Difficulties with the Direction of Magnetic Force on a Charged Particle

Abstract:

In a series of tests administered to introductory physics students, we examine how students answer questions about the direction of the magnetic force on a charged particle. Data were taken over a period of 17 weeks using differing representations of magnetic field. Following instruction, a significant proportion of answers (approximately 30% given a magnetic pole representation of field and 20% given field line ) coincided with an overall sign error. Potential sources of sign error (e.g. "left-hand-rule," physical discomfort, non-commutativity of cross products) were investigated via additional test questions and student interviews. Evidence from these additional experiments suggests that the sign errors are not systematic within students, but vary randomly. For example, students using the "left-hand-rule" would consistently answer with a sign error, while students who believe the cross product is commutative would answer with either the correct force or an overall sign error.